Patent Document 1 below discloses a drive system for an electrically driven dump truck in which the engine rotational speed is set to a medium rotational speed when the shift lever is placed in the forward (F) position or the reverse (R) position (see claim 2). With this drive system, good responsiveness and acceleration can be obtained when the truck starts moving or when the driver depresses the accelerator pedal.
However, when the shift lever is placed in the forward (F) position or the reverse (R) position, the engine is always maintained at the speed equal or larger than the medium rotational speed. This means that the engine keeps rotating at the medium rotational speed even when a minimum rotational speed is enough, that is, when the truck is going down a hill, coasting, or decelerating, or when the truck stands still by the driver stepping on the brake pedal. In such cases, fuel is wasted, and the noise to the driver as well as to the outside is increased.
On the other hand, according to claim 3 of Patent Document 1, the engine speed is set to a minimum rotational speed when the depressed amount of the accelerator pedal is in the range of 0 to a predetermined small amount, thereby preventing the occurrence of such problems.